The present invention relates to a method of providing enhanced characters better suited for being displayed on substantially low-resolution displays/screens.
The present invention also relates to a device providing enhanced characters better suited for being displayed on substantially low-resolution displays/screens.
Additionally, the invention relates to a method of displaying enhanced characters in a portable device comprising a memory and a display, using relatively little real-time memory and relatively little real-time processing power, and a portable device for displaying enhanced characters in a portable device, comprising a memory and a display, using relatively little real-time memory and relatively little real-time processing power.
When displaying characters on certain types of displays/screens, the typeface designer is typically severely limited by the low number of display pixels available, thereby making the displayed characters appear very simple or jagged. This is especially true for low-resolution displays such as those used in mobile terminals/phones, PDAs, etc.
One technique of improving a perceived smoothness of displayed characters on a display/screen is the well-known technique of anti-aliasing, using shades of grey where font designers would like to show only ‘part’ of a pixel. The perceived smoothness of displayed characters is obtained by the fact that a viewer's eyes will tend to average two adjacent grey pixels to see one in the ‘middle’, i.e. the two adjacent pixels are perceived as a single pixel located and with a color intensity/grey-level in the middle of the two adjacent pixels. However, anti-aliasing has the side effects, especially for small types/characters, that the characters become blurred and the readability is greatly reduced.
Another technique of improving the display of characters is the well-known technique of using sub-pixel rendering. Sub-pixels are a number of smaller pixels making up a single ordinary pixel, where each sub-pixel is associated with one of the three primary colors (red, green or blue). The human eye is not capable of registering closely spaced colors individually, since the vision system deliberately mixes these three primary colors in combination to form intermediates dependent on the intensity of each of the three primary colors.
Sub-pixel rendering only works with full effect on color displays where the red, green, blue components are made up of ‘sub-pixels’, i.e. colored strips, like an LCD display, etc. The ordering of the sub-pixels is typically red-green-blue although some are blue-green-red. However, fonts using sub-pixels shown on other types of displays like CRTs, grey-scale LCD displays, etc. will also be better perceived due to the inherent well-known anti-aliasing effect of sub-pixels.
An LCD screen with a given horizontal pixel resolution (e.g. 800 pixels) actually has a horizontal sub-pixel resolution three times greater (e.g. 2400 single color sub-pixels) when using sub-pixels. Sub-pixels may then be used to smooth jagged contours, lines, etc. by using the knowledge of the given ordering of the primary color and the corresponding sub-pixels and by ‘borrowing’ sub-pixels from adjacent whole pixels, thereby enabling fine-tuning of placement, width, etc. of a contour, character, etc. with a three times greater horizontal accuracy. However, the pixels along a contour would be non-white (due to the use of sub-pixels), but the human eyes would still perceive them as absolutely white, since the color of the sub-pixel is immediately adjacent to the other primary colors (e.g. red is adjacent to green and blue).
See e.g. http://grc.com/ctwhat.htm as pr. 2/11-2001 for further details regarding anti-aliasing and sub-pixel rendering.
However, both of the above techniques typically rely on the fact that the typeface is described by curve definitions, outlined fonts, etc. which requires a relative large amount of memory for storage. Additionally, the processing power required to render them (i.e. calculate what pixels to color) in real-time is quite substantial, which also requires a relatively great power consumption of a device performing the technique(s).